1. Field of the Invention
The present invention relates to a data output driver and output driving method, and more particularly to an output driver and output driving method, which compensate for the attenuation of transmission data during data communication.
2. Description of Related Art
Transmission data generated by a transmission device is transmitted to a reception device through a transmission line. The transmission device is typically provided with an output driver for outputting the transmission data. Transmission data is composed of a plurality of data bits to be consecutively transmitted. In the case of a data bit having a logic state differing from that of a previous data bit, there may occur a phenomenon where a rising or falling edge of the data bit is not sufficiently developed. The phenomenon, due to the previous data bit, may be referred to as Inter-Symbol Interference (hereinafter referred to as “ISI”). Due to ISI, attenuation of transmission data may occur. The ISI may further increase when the data bit having the logic state differing from that of the previous data bit is transmitted immediately after several data bits having the same logic state have been transmitted.
Various types of output drivers for compensating for the attenuation of transmission data caused by ISI have been developed.
FIG. 1 is a diagram showing an example of an output driver. FIG. 2 is a timing diagram showing the signals of the output driver of FIG. 1.
In an output driver 10 in FIG. 1, a bit shifter 11 shifts input data IDAT1 by one bit period and generates shifted data SDAT1. Further, a data adder 13 performs an operation of Equation [1] and generates output data ODAT1,V(ODAT1)−a*V(SDAT1)   [1]where V(ODAT1), V(IDAT1) AND V(SDAT1) denote the voltage levels of the output data ODAT1, the input data IDAT1 and the shifted data SDAT1, respectively. Further, “a” denotes a positive constant.
As shown in FIG. 2, in the output data ODAT1, the swing range of one bit value increases whenever the logic state of the output data ODAT1 is transitioned. Therefore, the attenuation of the output data ODAT1 is mitigated due to the increasing swing range.
FIG. 3 is a diagram showing another example of an output driver. FIG. 4 is a timing diagram showing the signals of the output driver of FIG. 3.
In the output driver 20 of FIG. 3, a delay unit 21 delays input data IDAT2 and generates delayed data DDAT2. Further, a data adder 23 performs an operation of Equation [2] and generates output data ODAT2,V(ODAT2)=V(IDAT2)−b*V(DDAT2)   [2]where V(ODAT2, V(IDAT2) and V(DDAT2) denote the voltage levels of the output data ODAT2, the input data IDAT2 and the delayed data DDAT2, respectively. Further, “b” denotes a positive constant.
As shown in FIG. 4, the initial voltage level of the output data ODAT2 is intensified whenever the logic state of the output data ODAT2 is transitioned. The attenuation of the output data ODAT2 is mitigated due to the intensified initial voltage level.
In the output drivers shown in FIGS. 1 and 3, the input data IDAT1 and IDAT2 and the output data ODAT1 and ODAT2 operate at a high voltage higher than a voltage level Vh in a logic H state, and at a low voltage lower than a voltage level V1 in a logic L state. The output drivers of FIGS. 1 and 3 need to include circuits for generating the high voltage and the low voltage.
Therefore, a need exists for an output driver and output driving method that compensate for the attenuation of transmission data during data communication without circuits for generating the high voltage and the low voltage.